Patent EP-0032205-B1 (EP)
IPC: H04M9/04
Filed: 1980-12-09
Granted: 1983-06-22
Abstract: 1. A key-controlled system for alternate, simultaneous or loud-speaking oral communication in which system each subscriber's station is adapted to be connected with a predetermined number of further subscriber's stations, and in which the connecting-through extension of the call and transmission circuits is established automatically through a central switchboard to which subscriber's stations (Sp1-Spn) are connected through line and connecting circuits (L1-Lm), and in which a micro-computer (CPU, RAM, ROM) is arranged, said micro computer being connected, through input and output units (EA) for receiving and emitting D.C. signals, with said call and transmission circuits arranged within said central switchboard on three different types of plug-in units, each type comprising at least one plug-in unit, namely line units (LK) having coupling circuits arranged thereon through which coupling circuits a D.C. connection is established between each line and one of the input and output units, junction units (VK) having arranged thereon an electronically controllable connection switching device for each of the predetermined possibilities of connection, the control input of said connection switching device being connected with one of the input and output units, and subscriber's station units (SpK) having arranged thereon a transmitter (Ü1-Ü4) for each of the subscriber's stations (Sp1-Spn), the primary winding (I) of said transmitter being connected with one each of said subscriber's stations, whereby a center tapping of said primary winding (I) is adapted to be connected to a voltage source through one of the input and output units (EA), and the secondary winding (II) of said transmitter being adapted to be connected, by means of a predetermined selection of the electronically controllable connection switching devices (S12, S13 ... S34), with the secondary winding of the selected further transmitters, and in which system the connecting-through extension of the line and connecting circuits is carried out in program-controlled manner by the micro-computer (CPU, RAM, ROM), characterized in that, additionally, at least one subscriber's station (SpO) is connected to the central switchboard through a four-wire circuit (VL1-VL2), whereby a call transmitter (RS) for emitting coded call signals, a call keyboard (TA1) for controlling said call transmitter (RS), a hearing and speaking equipment (HS), as well as a key-controlled switching mechanism (A, a1, a2) for changing said hearing and speaking equipment over to "speak" and for switching on and off an indicator (LA, LB) for call and busy signals, are arranged in the subscriber's station (SpO), and whereby at least one plug-in unit of a further type is privided in the central switchboard, namely a four-wire circuit unit (VLK) having arranged thereon a call receiver (RE) for receiving the coded call signals, and a decoder (DEK) for transposing the call signals to a predetermined number of circuits (L17-L20), each output of said decoder (DEK) associated with one circuit, being connected with one input (EAVL) of the input and output units (EA) and with one input of an AND-gate (U1, U4) the other input of which is connected with the output of said input and output units (EAVL) corresponding to said one circuit, and the outputs of all AND-gates (U1, U4) associated with one decoder (DEK) being connected with the center tapping of the primary winding of the transmitter (ÜO) associated with the subscriber's station (SpO) and arranged on one of the subscriber's station units (SpK), and that, through the first pair of lines (LP1) of the four-wire circuit, the call transmitter (RS) is connected with the call receiver (RE), while the operational voltage inputs of the subscriber's station (SpO) are connected with a voltage source (Ub) arranged in the central switchboard and while, through the second pair of lines (LP2) of said four-wire circuit, the hearing and speaking equipement (HS) is connected with the primary winding of the transmitter (ÜO) associated therewith, the indicators (LA, LB) for call and busy signals being connected, through the center tapping of the primary winding of said transmitter (ÜO), with the outputs (ASpO or EAVL) of the input and output units (EA) for emitting call and busy signals.